High frequency (HF) electromagnetic wave emitting or receiving devices may be provided in form of one or more integrated circuits. The integrated circuits may be arranged on a wiring board, e.g., a printed circuit board (PCB). An emission or a reception antenna that is suitably coupled to the integrated circuits may be arranged on the wiring board or be integrated therein. The wiring board may comprise one or more conductive layers and one or more isolating layers arranged atop each other in an alternating manner so that there is an isolating layer between each pair of adjacent conductive layers. Various electronic components such as conductors, capacitors, inductors, or microstrip lines may be integrated in the conductive layers.
An isolating layer may comprise or consist of a suitable dielectric isolating material. Isolating materials having a relatively low dielectric constant may be preferred in the case of high frequency applications. For instance, an isolating layer arranged next to a conductive layer comprising a high frequency signal line may be made of an isolating material having a dielectric constant of approximately 3, whereas isolating layers not adjacent to any high frequency signal line may be made of an isolating material having a dielectric constant of, e.g., 4.4. Examples of isolating materials with suitably low dielectric constants include the materials RT5880 and RO3003 produced by the Rogers Corporation (USA). These materials are known to be suitable for high frequency applications involving frequencies up to 40 gigahertz or even higher frequencies. However, a variety of other isolating materials and notably some Teflon-based materials may also be suitable.
In this application, the expressions “special isolating material” and “normal isolating material” are used to distinguish between two different isolating materials, wherein the special isolating material has a lower dielectric constant than the normal isolating material. Furthermore, the special isolating material may have a much lower loss tangent at high frequencies, which may be beneficial for operation at higher frequencies, e.g., above 1 GHz. The special and the normal isolating materials may, for instance, have a dielectric constant of approximately 3 and approximately 4.4, respectively. Today's special isolating materials tend to be more expensive than normal isolating materials.